Add kredits API with wallet balance endpoint

app/controllers/api/base_controller.rb

@@ -0,0 +1,5 @@
+class Api::BaseController < ApplicationController
+
+  layout false
+
+end

app/controllers/api/kredits_controller.rb

@@ -0,0 +1,12 @@
+class Api::KreditsController < Api::BaseController
+
+  def onchain_btc_balance
+    btcpay = BtcPay.new
+    balance = btcpay.onchain_wallet_balance
+    render json: balance
+  rescue
+    render json: { error: 'Failed to fetch wallet balance' },
+           status: 500
+  end
+
+end